White opaque films with thicknesses in the range between 10 and 100 μm are well known. U.S. Pat. No. 4,780,402 describes a light-sensitive imaging material comprising an opaque carrier film of polyester which has a high proportion of barium sulfate in the range from 5 to 50% by weight. The particle size of the barium sulfate used according to the teaching of the US patent is in the range from 0.5 to 10 μm.
EP 1 125 967 (whose United States equivalent is published as United States Published Application No. 2003/017317) relates to a white opaque film with low transparency composed of a crystallizable thermoplastic whose thickness is in the range from 10 to 500 μm. The film contains 0.2 to 40% by weight of barium sulfate with a mean particle size in the range from 0.1 to 5 μm as a white pigment, and also an optical brightener, and is notable for good stretchability, for low transparency, and for very good optical and mechanical properties. The barium sulfate and/or the optical brightener are either incorporated directly into the thermoplastic at the raw material manufacturer, or metered in as a masterbatch in the course of film production. Owing to its combination of properties, the film is suitable for comparable applications as described above in EP 1 125 966. However, for the desired translucence, the transparency of the film is unsuitable for specific applications in the exterior sector such as exterior glazing.
EP 1 842 663 (whose United States equivalent is published as United States Published Application No. 2007/240075) describes a white opaque coextruded film which, as well as white pigments, comprises at least one antiblocking agent in the outer layers for better windability. However, the transparency of this film is very low, similarly to the case of EP 1 125 967. Owing to its low transparency, this prior art film cannot be used for glazing either, and especially not in the exterior sector.